An aircraft turbine engine generally comprises a fuel tank, a combustion chamber and a fuel system adapted to regulate the flow of fuel from the fuel tank towards the combustion chamber.
The fuel system comprises a set of fuel nozzles disposed in the combustion chamber, a fuel pump for pressurising from the fuel tank, a fuelmetering unit (FMU) for controlling the flow of fuel to the nozzles, and a fuel supply circuit fluidically connecting the fuelmetering unit to the fuel nozzles.
During start-up of the turbine engine, fuel is pumped from the fuel tank to the FMU by the pump, and once there is enough start-up pressure, the FMU sends fuel to the nozzles.
The fuel system can comprise multiple flow paths. For example, a fuel system can comprise two sets of nozzles (a main set and a secondary set), pipes for each set and a flow divider valve arranged downstream of the FMU.
In such systems, fuel is delivered to the primary and secondary nozzles as a function of the speed of the turbine engine. For example, during start-up of the turbine engine, fuel is initially supplied only to the primary nozzles by means of a primary supply circuit. However, once fuel coming from the primary fuel nozzles which burns evenly and satisfactorily, fuel is then also supplied to the secondary nozzles by means of a secondary supply circuit. In other terms, the primary supply circuit supplies a pilot flow which triggers the combustion process, while the secondary supply circuit has a main flow rate, adapted to complete and intensify the combustion process, once the pilot flow is burning constantly.
To reduce problems linked to the presence of residual fuel in the conduits of the fuel system after the turbine engine has been shut-down, document U.S. Pat. No. 5,809,771 proposes purging the conduits of the fuel system by means of a valve connected to the pilot and main nozzles, adapted to suction, store then return fuel when the turbine engine is stopped.
But operation of the fuel system is directly controlled by the pressure available at the outlet of the FMU, which does not sufficiently adapt the flow rate to the speed of the turbine engine, or evolve the fuel distribution values over time, for example in considering the ageing of the turbine engine. Also, in document U.S. Pat. No. 5,809,771 the fuel is purged only when the turbine engine is shutdown. Also, using two fuel supply circuits often involves different pressure losses between the two circuits.
Finally, with the main supply circuit being on flow intermittent rate, coke risks forming in the conduits under the effect of severe conditions which the fuel system can undergo, especially temperature.
Document EP 2 535 644 proposes a fuel system for a turbine engine, adapted to inject fuel into a combustion chamber of the turbine engine comprising a pilot circuit, a main circuit and a flow rate regulator. However, this fuel system comprises no means for preventing the formation of coke when the main circuit is not passing.
Document EP 2 063 087 as such also describes a fuel system for a turbine engine, adapted to inject fuel into a combustion chamber of the turbine engine comprising a pilot circuit, a main circuit and a flow rate regulator. This document also proposes purging the circuits when the engine is stopped. The purging means are however not specified.
Finally, document EP 1 988 267 describes a fuel system for a turbine engine, adapted to inject fuel into a combustion chamber of the turbine engine comprising a pilot circuit, two main circuits, a flow rate regulator and a purge tank. The configuration of the fuel system is such that here too it purges the main circuits only when the turbine engine is shutdown.